Low compression set silicone elastomers

ABSTRACT

The present invention provides novel vinyl containing organopolysiloxane elastomers which possess excellent low compression set and heat aging characteristics and which can advantageously be formulated into liquid silicone elastomer moldable compositions.

This is a continuation of Ser. No. 08/450,293 filed on May 25, 1995 nowabandoned which is a continuation of Ser. No. 07/824,849 filed on Jan.23, 1992, also now abandoned.

The present invention relates to a fast curing silicone elastomercomposition. More particularly, the present invention relates to vinylcontaining silicone elastomer compositions which are useful as fastcuring compounds and as liquid injection moldable compositions. Thesenovel silicone elastomer compositions of the present invention haveexcellent low compression set and heat aging characteristics.

BACKGROUND OF THE PRESENT INVENTION

Polyorganosiloxane compositions that can be cured to form elastomericproducts are well known in the art. Modified organopolysiloxanes havebeen prepared in the prior art by polymerizing monomers containingaliphatic unsaturation in the presence of organopolysiloxanes containingterminal hydroxyl or hydrolyzable groups and free radical initiators.

Rufer et al., U.S. Pat. No. 4,536,553, disclose improving the flex lifeof silicone elastomers having olefinic unsaturation by mixing with thesilicone elastomer a vinyl acetate ethylene copolymer in the presence ofa free radical catalyst at an elevated temperature.

Jensen, U.S. Pat. No. 4,929,669, in an attempt to achieve lowcompression set, teaches the presence of a vinyl-specific peroxide in aliquid diorganopolysiloxane containing at least two silicon-bonded vinylradicals per molecule which are curable to elastomers by a platinumcatalyzed hydrosilation reaction. However, the combination tends toretard the platinum cure.

Kroupa et al., U.S. Pat. No. 4,500,659, disclose an extrudable, curablesilicone elastomer composition prepared by reacting a reinforcing silicafiller in a high viscosity marginally extrudable silicon elastomercomposition with a liquid fluorinated polyorganosiloxane.

Special mention is made of Nelson, U.S. Pat. No. 3,284,406 whichdiscloses a mixture consisting essentially of (1) a polysiloxane of theformula ##STR1## in which R and R' are phenyl or methyl and at least 80mole percent of the R' groups are methyl, said siloxane (1) having aviscosity of from 500 to 500,000 centipoise inclusive at 25° C.; (2)from 5 to 50 percent by weight based on the weight of (1) and (2) of acopolymer of SiO₂, Me₃ SiO₀.5 and Me₂ ViSiO₀.5 siloxane units in whichcopolymer there is from 1.5 to 3.5 percent by weight vinyl groups basedon the weight of (2) and in which copolymer (2) the ratio of total Me₃SiO₀.5 and Me₂ ViSi₀.5 to SiO₂ units is from 0.6:1 to 1:1; (3) acompound compatible with (1) and (2) which is a siloxane containing from0.1 to 1.7 percent by weight silicon bonded hydrogen atoms the remainingvalences in (3) being satisfied by phenyl or methyl radicals, therebeing at least three silicon-bonded hydrogen atoms per molecule, and in(3) any hydrocarbon radicals attached to an SiH silicon beingessentially all methyl radicals, the amount of (3) being such that thereis from 0.75 mol of SiH per mol of vinyl radicals in (1) and (2) to 1.5mol of SiH per mol of vinyl radicals in (1) and (2); and (4) a platinumcatalyst.

Jeram et al., U.S. Pat. No. 3,884,866 disclose an organopolysiloxanecomposition comprising a first component comprising a mixture of twovinyl-containing polysiloxanes or blends of vinyl-containingpolysiloxanes one of which is a high viscosity polysiloxane and theother of which is a low viscosity polysiloxane, a filler and aneffective amount of a platinum catalyst; and a second componentcomprising a hydrogen-containing silane or polysiloxane.

Jeram et al., U.S. Pat. No. 4,340,709 disclose an addition curingsilicone composition with a low viscosity in the uncured state and highphysical strength in the cured state comprising a vinyl-containingdiorganopolysiloxane polymer, a platinum catalyst, a hydridecross-linking agent and a linear hydride coupler in which the viscosityof the linear hydride coupler varies from 1 to 1,000 centipoise at 25°C.

However, the prior art silicone elastomers, while providing good solventresistance and other physical properties suffer from such drawbacks aspoor heat aging and high compression set characteristics making themunsuitable for use in many applications, such as gaskets. It wouldtherefore represent a notable advance in the state of the art if asilicone composition could be provided having excellent heat stabilitycharacteristics, rendering the composition useful where heat stabilityis important such as in gasketing, coatings and potting applications asmeasured by oven aging and percent compression set. Unexpectedly, thecompositions of the present invention satisfy such a long felt need,exhibiting excellent low compression set and heat aging characteristics.Such surprising results are shown in the working examples hereinbelow.

SUMMARY OF THE INVENTION

According to the present invention there is provided a fast curingsilicone composition having low compression set and excellent heat agingproperties comprising a silicone component of the general formula:MM^(vi) Q wherein M is R₃ SiO_(1/2) ; M^(vi) is CH₂ =CHR₂ SiO_(1/2) ;and Q is SiO_(4/2) where R, R¹ and R² are independently each alkyl offrom 1 to about 8 carbon atoms or cycloalkyl or cycloalkenyl of from 5to about 10 carbon atoms or aryl of from 6 to about 12 carbon atoms andwherein the ratio of M and M^(vi) units to Q units ranges from 1.1 toabout 2.0.

Also according to the present invention there is provided a fast curingliquid silicone elastomer organopolysiloxane composition comprising (a)a first silicone component of the formula MM^(vi) Q wherein M is R₃SiO_(3/2) ; M^(vi) is R¹ =R² R₂ SiO_(3/2) ; and Q is SiO_(4/2) where Ris alkyl of from 1 to about 8 carbon atoms or cycloalkyl or cycloalkenylof from 5 to about 10 carbon atoms or aryl of from 6 to about 12 carbonatoms and wherein the ratio of M and M^(vi) units to Q units ranges from1.1 to about 2.0; (b) a second component comprising a vinyl-containingdiorganopolysiloxane having the formula ##STR2## where Vi is vinyl, andR³ and R⁴ are monovalent hydrocarbon radicals other than olefinicradicals and t varies such that the viscosity of thediorganopolysiloxane varies from 100 to 200,000 centipoise at 25° C.;(c) from 0.1 to 50 parts per million of the total organopolysiloxanecomposition of a platinum catalyst; and (d) from 0.1 to 25 parts byweight of a curing agent selected from the group consisting of hydrogencontaining silanes and hydrogen containing polysiloxanes and mixturesthereof.

According to the present invention there is also provided a fast curingsilicone composition having low compression set of the general formula:MM^(vi) QD wherein: M is R₃ SiO_(1/2) ; M^(vi) is CH₂ =CH₁ R₂ SiO_(1/2); Q is SiO_(4/2) ; and D is R₂ SiO_(2/2) in an amount sufficient tolower the compression set by at least about 20% and where R is alkyl offrom 1 to about 8 carbon atoms or cycloalkyl or cycloalkenyl of from 5to about 10 carbon atoms or aryl of from 6 to about 12 carbon atoms.

Also according to the present invention there is provided a fast curingliquid silicone elastomer organopolysiloxane composition comprising (a)a first silicone component of the formula MM^(vi) QD wherein: M is R₃SiO_(1/2) ; M^(vi) is CH₃ =CH₂ R₂ SiO_(1/2) ; Q is SiO_(4/2) ; and D isR₂ SiO_(2/2) in an amount sufficient to lower the compression set by atleast about 20% and where R is alkyl of from 1 to about 8 carbon atomsor cycloalkyl or cycloalkenyl of from 5 to about 10 carbon atoms or arylof from 6 to about 12 carbon atoms; (b) a second component comprising avinyl-containing diorganopolysiloxane having the formula ##STR3## whereVi is vinyl, and R³ and R⁴ are monovalent hydrocarbon radicals otherthan olefinic radicals and t varies such that the viscosity of thediorganopolysiloxane varies from 100 to 200,000 centipoise at 25° C.;(c) from 0.1 to 50 parts per million of the total organopolysiloxanecomposition of a platinum catalyst; and (d) from 0.1 to 25 parts byweight of a curing agent selected from the group consisting of hydrogencontaining silanes and hydrogen containing polysiloxanes and mixturesthereof.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

Novel silicone compositions which cure fast to low compression setelastomers exhibiting excellent heat aging properties are provided bythe present invention.

In one aspect of the present invention, the silicone component (a)useful in the practice of the present invention is of the generalformula:

    MM.sup.vi Q                                                (1)

wherein M is R₃ SiO_(1/2) ; M^(vi) is CH₂ =CHR₂ SiO_(1/2) ; and Q isSiO_(4/2) where R is alkyl from 1 to about 8 carbon atoms or cycloalkylor cycloalkenyl of from 5 to about 10 carbon atoms or aryl of from 6 toabout 12 carbon atoms.

Preferably, R is selected from hydrocarbon radicals such as methyl,ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, cyclopentyl,cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, cyclodecyl, benzyl,phenyl, cumyl, xylyl, tolyl and the like. Most preferred are methyl andphenyl.

It is essential to the present invention that the silicone polymers havea ratio of M and M^(vi) units to Q units of above 1.1, preferably from1.1 to about 2.0, and more preferably from 1.1 to about 1.5. Thosesilicone polymers with a ratio of M and M^(vi) units to Q units lessthan 1.1, particularly less than 1.0, do not exhibit the low compressionset characteristics of the compositions of the present invention, andare therefore not useful as a gasket material.

In another aspect of the present invention, the silicone component (a)useful in the practice of the present invention is of the generalformula:

    MM.sup.vi QD                                               (2)

wherein M is R₃ SiO_(1/2) ; M^(vi) is CH₂ =CHR₂ SiO_(1/2) ; Q isSiO_(4/2) ; and D is R₂ SiO_(2/2) ; wherein the amount of D in thesilicone polymer is an amount sufficient to lower the compression set byat least about 20% and where R, is alkyl of from 1 to about 8 carbonatoms or cycloalkyl or cycloalkenyl of from 5 to about 10 carbon atomsor aryl of from 6 to about 12 carbon atoms.

Preferably, R is selected from hydrocarbon radicals such as methyl,ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, cyclopentyl,cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, cyclodecyl, benzyl,phenyl, cumyl, xylyl, tolyl and the like. Most preferred are methyl andphenyl.

It is essential to the practice of the present invention that when thesilicone polymers of formula (2) are employed, the ratio of D units to Qunits is less than about 8:1, preferably from about 0.5:1 to about 8:1,more preferably from about 0.6:1 to about 5:1, and most preferably fromabout 0.9:1 to about 2:1. Where the ratio of D units to Q units isgreater than 10:1, the composition gels and is not useful in liquidsilicone elastomer formulations.

The novel silicones of formulae (1) and (2) of the present invention areprepared by methods known to those skilled in the art.

The compositions of the present invention can be formulated into fastcuring liquid silicone elastomer (LSE) organopolysiloxane compositions.These LSE compositions typically contain an additional componentcomprising from about 25 to about 99 parts by weight of a base vinylcontaining diorganopolysiloxy polymer having a viscosity varying from100 to 200,000 centipoise at 25° C., where the (CH₃)₂ ViSiO₀.5 contentgenerally varies from 0.005 to 3.5 and more preferably varies from 0.015to 2.6 mole percent. The organic groups are monovalent hydrocarbonradicals. Preferably, the organo groups are selected from alkyl radicalssuch as methyl, ethyl, propyl, etc.; alkenyl radicals such as vinyl,allyl, etc.; cycloalkyl radicals such as cyclohexyl, cycloheptyl, etc.;mononuclear aryl radicals such as phenyl, ethylphenyl, etc.; andhaloalkyl radicals such as 3,3,3-trifluoropropyl. Most preferably themonovalent hydrocarbon radical is selected from an alkyl radical of 1 to8 carbon atoms or phenyl. Preferably there is no vinyl or alkenylradicals in the central part of the polysiloxane chain of the base vinylcontaining polymer. This is especially important in the instant casesince the vinyl groups in the internal position of the polymer chainwill tend to crosslink rather than be extended. Accordingly, preferably,the base vinyl containing polymer does not have any vinyl groups orolefinic unsaturated groups in the internal position of the polymerchain but just has vinyl in the terminal position of the polymer chain.

A particularly preferred second component comprises a vinyl-containingdiorganopolysiloxane having the formula ##STR4## where Vi is vinyl, andR³ and R⁴ are monovalent hydrocarbon radicals other than olefinicradicals and t varies such that the viscosity of thediorganopolysiloxane varies from 100 to 200,000 centipoise at 25° C.

Preferably R³ and R⁴ are selected from alkyl radicals of 1 to 8 carbonatoms such as methyl, ethyl, propyl; mononuclear aryl radicals such asphenyl, methylphenyl, ethylphenyl; cycloalkyl radicals such ascycloheptyl; and haloalkyl radicals such as 3,3,3-trifluoropropyl. Mostpreferably, the R³ and R⁴ radicals are selected from alkyl radicals of 1to 8 carbon atoms and phenyl.

The polymers of formula (3) are generally prepared by equilibrating theappropriate cyclo tetrasiloxane with the appropriate vinyl terminatedlow molecular weight polysiloxane chainstoppers. The chainstopper ispreferred for such equilibration reaction and is preferably a lowmolecular weight vinyl terminated polysiloxane compound such as adisiloxane, trisiloxane, tetrasiloxane and so forth. These low molecularweight vinyl terminated polysiloxane polymers are produced byhydrolyzing the appropriate chlorosilanes particularly vinyldiorganochlorosilanes along with diorganodichlorosilanes to produce thedesired chainstopper. This chainstopper is then taken in a relativelypure form and equilibrated along the cyclotetrasiloxanes with theappropriate substitute groups in the presence of a catalyst to producethe desired vinyl terminated diorganopolysiloxane polymer having aviscosity varying from 100 to 200,000 centipoise at 25° C. The catalystthat is utilized is preferably a basic catalyst, such as KOH,tetramethyl ammonium hydroxide or sodium hydroxide. When theequilibration has proceeded to the point where about 85% of thecyclopolysiloxanes have been converted to the linear polymer, the basiccatalyst is neutralized with an acid to leave behind the linear polymer.Preferably, excess cyclics are stripped off so that the linear polymerwill have a low volatile content and be relatively pure.

The compositions of the present invention may also include an effectiveamount of a filler. Preferred fillers are those known to those skilledin the art, such as, titanium dioxide, lithopone, zinc oxide, zirconiumsilicate, silica aerogel, iron oxide, diatomaceous earth, calciumcarbonate, fumed silica, silazane treated silica, precipitated silica,glass fibers, magnesium oxide, chromic oxide, zirconium oxide, aluminumoxide, alpha quartz, calcined clay, asbestos, carbon, graphite, cork,cotton, synthetic fibers and mixtures of any of the foregoing.Particularly preferred are fumed silica, silazane treated silica,calcium carbonate and mixtures thereof.

The compositions of the present invention further comprise acrosslinking or curing agent such as a silicone hydride polysiloxane.The SiH-containing polysiloxanes contemplated for use herein ascrosslinking agents are comprised primarily of compounds having thegeneral formula:

    M.sup.H D.sub.x D.sub.y.sup.H M.sup.H                      ( 4)

wherein each M^(H) is independently either hydrogen or a monovalenthydrocarbon radical of from 1 to 8 carbon atoms, with a sufficientnumber of M groups being hydrogen to provide at least 1% by weighthydrogen as hydrogen per molecule; and where D^(H) is an SiO-- unit.Such polysiloxanes will include, for example, cyclic polymers such assymtetrahydrotetramethylcyclotetrasiloxane, or linear polymers such asalkylhydrogensiloxane fluids or polydialkyl-alkylhydrogen siloxanecopolymers. Particularly useful as crosslinking agents for the presentinvention are dimethyl-hydrogen chainstopped, polydimethyl,polymethylhydrogen siloxane fluids having from approximately 10% to 100%SiH groups and having a viscosity in the range of from about 15 to about500 centipoise at 25° C.

The compositions of the present invention may also comprise a curingagent, which can be present in amounts ranging from 0.1 to 25 parts byweight and can be selected from the group consisting of hydride resinshaving only terminal hydrogen atoms or a hydride polysiloxane havinghydrogen atoms in the terminal and internal portion of the polysiloxanechain. Accordingly, there may be utilized a hydride resin having theformula: ##STR5## units and SiO₂ units where the R⁵ +H to Si ratiovaries from 1.0 to 2.7 or a hydride resin of the formula ##STR6## units,SiO₂ units and R⁷ R⁷ SiO units where the R⁶ +R⁷ +H to Si ratio variesfrom 1.2 to 2.7 and where R⁵, R⁶ and R⁷ are monovalent hydrocarbonradicals other than olefinic hydrocarbon radicals.

Most preferably, R⁵, R⁶ and R⁷ are selected from alkyl radicals of 1 to8 carbon atoms; mononuclear aryl radicals such as phenyl, ethylphenyl,etc.; cycloalkyl radicals such as cycloheptyl, cyclooctyl; etc.;haloalkyl radicals such as 3,3,3-trifluoropropyl, etc. Most preferably,R⁵, R⁶ and R⁷ are selected from alkyl radicals of 1 to 8 carbon atomsand phenyl radicals. It is important that there be no aliphaticunsaturated groups for the R⁵, R⁶ and R⁷ radicals. These hydrides can besimply produced in the controlled hydrolysis of the correspondinghydride chlorosilanes in the presence of a hydrocarbon organic solvent.For the resin containing only monofunctional units and tetrafunctionalunits, a hydrogen diorganochlorosilane is hydrolyzed along with atetrachlorosilane to produce the desired resin. In the case of the resincontaining the monofunctional siloxy units, the difunctional siloxyunits and the tetrafunctional siloxy units, there is hydrolyzed ahydrogen diorgano dichlorosilane, a tetrachlorosilane and adiorganodichlorosilane in the desired ratios to produce the desiredresins. For more information as to the process by which these resins areproduced, one is referred to Jeram, U.S. Pat. No. 4,040,101.

In other embodiments of the present invention, there may be used alinear hydrogen containing polysiloxane as the curing agent.Accordingly, there may be utilized a linear hydride polysiloxane havingthe formula: ##STR7## where R⁸ is a monovalent hydrocarbon radical otherthan an olefinic hydrocarbon radical and p and q vary such that thepolymer has a viscosity that varies from 1 to 1000 centipoise at 25° C.and wherein the polysiloxane has from 0.04 to 1.7 percent by weighthydrogen.

Such a hydride polymer of Formula (7) above is produced by equilibratingthe appropriate hydrogen cyclopolysiloxane with the appropriate cyclopolysiloxane containing R⁸ substituent groups, in the presence ofdisiloxane, trisiloxane and other low molecular weight lineartriorganosiloxy end-stopped chain stoppers. Alternatively, the processcomprises hydrolyzing the appropriate chlorosilanes in water alone or inthe presence of a hydrocarbon solvent to produce a mixture of cyclic andlinear hydride polymers of Formula (7) above. The cyclics can then bestripped off.

The curing reaction which takes place between the vinyl-functionalpolysiloxane base polymer and the SiH-containing crosslinking agent isan addition cure reaction, known as hydrosilation. The compositions ofthe present invention may be thermally cured by means of a platinumcatalyzed crosslinking reaction between the vinyl groups of the basepolymer and the SiH reaction sites of the crosslinker.

Suitable hydrosilation catalysts to be employed in the present inventionare known to persons skilled in the art and include metal catalystsutilizing such precious metals as ruthenium, rhodium, palladium, osmium,iridium and platinum, and complexes of these metals. Especiallypreferred are platinum metal catalysts. Examples of such hydrosilationcatalysts are described in, inter alia, Lamoreaux, U.S. Pat. No.3,220,972; Karstedt, U.S. Pat. Nos. 3,715,334; 3,775,452 and 3,814,730;Ashby, U.S. Pat. Nos. 4,421,903; and 4,288,345; and Saruyama et al.,U.S. Pat. No. 5,057,476.

The selection of the particular catalyst will depend upon such factorsas speed of reaction desired, expense, useful shelf-life, usefulpot-life and the temperature at which the cure reaction is to takeplace. The amount of catalyst employed is not critical, so long asproper crosslinking is achieved; however, as indicated above, the highcost of these precious metal catalysts makes their conservative use apractical requirement. As with any catalyst, it is preferable to use thesmallest effective amount possible. For the coating compositionsdescribed herein, enough total catalyst is used to provide from about 10to about 500 parts per million of precious metal as precious metal.

The liquid silicone compositions (LSE) compositions of the presentinvention can be added to conventional liquid injection molding apparatifor forming plastic or rubber parts. The LSE compositions can also beused to form encapsulated parts with little waste. For liquid siliconeelastomer molding applications, it is desired that the uncured viscosityof the molding material be generally in the range of 10,000 to 2,000,000centipoise at 25° C. If the composition has this viscosity, it can bereadily forced into the molding chamber of a molding apparatus such as aliquid injection molding machine. Further, it is necessary for the LSEcomposition to be a fast curing composition. Upon being heated toelevated temperatures, the molded parts can be formed with rapidity. Thefaster the parts are formed by the liquid injection molding machine, thelower the cost of the formed part and the more economic the process.

In addition, the foregoing compounds of the present invention maycomprise from 100 to 100,000 parts per million of an inhibitor compoundselected from the group consisting of vinyl containing organocyclotetrasiloxanes such as methyl vinyl cyclotetrasiloxane,trialkylcyanurate, an alkyl maleate and mixtures thereof. Alsocontemplated for use herein as an inhibitor are acetylenic compounds asdescribed in Kookootsedes et al., U.S. Pat. No. 3,445,420. The exampleof alkyl maleate as an inhibitor in an addition curing siliconecomposition is, for instance, found in Eckberg, U.S. Pat. No. 4,256,870.With the exception of alkyl maleates, the other inhibitors arerelatively mild inhibitors which are utilized to give the composition,when it has been mixed into a single mixture, a certain amount of shelflife at room temperature so that the composition will cure at elevatedtemperatures, that is, temperatures about 150° to 200° C. in a matter ofseconds. However, if it is desired to employ the total composition in asingle package composition, there may also be utilized at least 0.001parts by weight per 100 parts by weight of the base polymer of aninhibitor compound having at least one hydroperoxy radical of theformula --C--O--O--H as disclosed in Bobear, U.S. Pat. No. 4,061,604.The hydroperoxy inhibitors allow all the ingredients to be mixed into asingle package and yet the composition will not cure at room temperaturefor periods as long as six months to 1 year or even more, but whenheated at elevated temperatures, those above 125° C., will cure in arapid manner. These heat cured compositions are suitable for making athermally stable gasket having a low compression set.

In accordance with the present invention, it is possible to have anaddition curing silicone composition having surprisingly excellent lowcompression set and heat aging characteristics and that has good tensilestrength, elongation, tear and durometer hardness. Further, thesecompositions are suitable to be formulated into liquid siliconeelastomer moldable compositions.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following examples illustrate the present invention. They are not tobe construed to limit the scope of the appended claims in any mannerwhatsoever.

EXAMPLES 1 AND 1A*

Two silicone compositions are prepared having the followingformulations.

                  TABLE 1                                                         ______________________________________                                        Example            1      1A*                                                 ______________________________________                                        Composition, pbw                                                              MM.sup.vi Q        25     25                                                  Ratio M + M.sup.vi :Q                                                                            1.5    1.0                                                 Vinyl end stopped  75     75                                                  high viscosity                                                                organopolysiloxane                                                            Platinum Catalyst.sup.a                                                                          20     20                                                  Hydride Crosslinker                                                                              3.5    3.5                                                 Properties                                                                    Compression set, % 10     85                                                  Heat Aging.sup.b   +1     +8                                                  ______________________________________                                         .sup.a In parts per million of platinum                                       .sup.b Oven heat aging at 177° C. for 70 hours, hardness change        points as measured in Shore A                                            

From Table 1 above it can be seen that compositions according to thepresent invention, having a M+M^(vi) :Q ratio of above 1.1, exhibithighly desirable low compression set and a vastly increased thermalstability over the compositions of the prior art, having a M+M^(vi) :Qratio of 1.0 or below. The significant improvements in these propertiesindicates that the compositions of the present invention will form asuperior gasket material.

EXAMPLE 2

The procedure of Example 1 is followed except that there is included 20parts by weight of treated fumed silica and 10 parts by weight ofMinusil filler. The product composition has a compression set value of20%.

EXAMPLE 3

The composition of Example 1 is formed into a gasket by heat curing thecomposition for 60 seconds at 177° C.

EXAMPLE 4

The composition prepared in Example 2 is formed into a gasket by heatcuring the composition for 60 seconds at 177° C.

EXAMPLES 5 AND 6

Two silicone compositions are made having the following formulations.

                  TABLE 2                                                         ______________________________________                                        Example            5      6                                                   ______________________________________                                        Composition, pbw                                                              MM.sup.vi QD       25     25                                                  Ratio D:Q          1.0    0.8                                                 Vinyl end stopped  75     75                                                  high viscosity                                                                organopolysiloxane                                                            Platinum Catalyst.sup.a                                                                          20     20                                                  Hydride crosslinker                                                                              3.5    3.5                                                 SiH/SiVi ratio     1.3    1.3                                                 Properties                                                                    Compression set, % 27     89                                                  Heat aging.sup.b   +2     +5                                                  ______________________________________                                         .sup.a In parts per million platinum                                          .sup.b Oven heat aging for 70 hours at 177° C., measured as change     in points in hardness (Shore A)                                          

From Table 2 above, it can be clearly seen that silicone compositions ofthe present invention having a ratio of D:Q of 0.8:1 or more havesignificantly improved compression set and heat aging properties overthose having a D:Q ratio of 0.8:1 or less. Such excellent propertiesmakes the compositions of the present invention eminently suitable asgasket materials.

EXAMPLES 7 AND 7A*

Two silicone compositions are prepared according to the followingformulations.

                  TABLE 3                                                         ______________________________________                                        Example            7      7A*                                                 ______________________________________                                        Composition, pbw                                                              MM.sup.vi OD.sup.a (D/Q 1:1)                                                                     25     --                                                  MQD.sup.vi (M/Q = 0.67)                                                                          --     25                                                  Vinyl end stopped  75     75                                                  high viscosity                                                                organopolysiloxane                                                            Platinum Catalyst.sup.b                                                                          20     20                                                  Hydride crosslinker                                                                              3.5    3.5                                                 Filler.sup.c       30     30                                                  Properties                                                                    Shore Durometer    58     60                                                  Tensile, psi       800    1100                                                % Elongation       400    600                                                 Tear strength, psi 130    250                                                 Compression set, % 27     90                                                  Heat Aging.sup.d   +1     +12                                                 ______________________________________                                         *Comparative Example                                                          .sup.a Dimethyl D units or a blend of dimethyl D units and methyl vinyl D     units                                                                         .sup.b In parts per million platinum                                          .sup.c Minusil (alpha quartz), fumed silica mixture                           .sup.d Change in hardness after heat aging for 70 hours at 177° C.     (Shore A)                                                                

From Table 3 above, it can readily be seen that filled compositions ofthe present invention exhibit much lower compression set and improvedheat aging over compositions of the prior art, thus making them a moresuitable material for gasket applications.

EXAMPLE 8

The procedure of Example 6 is followed and the composition is heat curedfor 60 seconds at 177° C. to form a gasket.

EXAMPLE 9

The procedure of Example 7 is followed and the composition is heat curedfor 60 seconds at 177° C. to form a gasket.

The above-mentioned patents and publications are hereby incorporated byreference.

Many variations of the present invention will suggest themselves tothose skilled in the art in light of the above detailed description. Forexample, a wide variety of fillers and/or inhibitors can be added to thecompositions of the present invention for their desired properties. Itis further within the scope of the instant invention to includeconventional additives, in desired amounts, such as gum cureaccelerators, controlled release agents, fillers, anti-microbial agents,pigments, dyes, mixtures thereof and the like, in the presentcompositions. All such obvious modifications are within the scope of theappended claims.

We claim:
 1. A fast curing silicone polymer resin composition having lowcompression set consisting essentially of:(a) a silicone component ofthe general formula:

    MM.sup.Vi QD

wherein M is R₃ SiO_(1/2), M^(Vi) is CH₂ =CH₂ R₂ SiO_(1/2), Q isSiO_(4/2), and D is R₂ SiO_(2/2) where each R is independently selectedand R is alkyl of from 1 to about 8 carbon atoms, cycloalkyl orcycloalkenyl of from 5 to about 10 carbon atoms or aryl of from 6 toabout 12 carbon atoms wherein the ratio of M and M^(Vi) units to Q unitsranges from 1.1 to about 2.0 and the ratio of D units to Q units is fromabout 0.5 to about 8; (b) a dimethyl vinyl chainstoppeddiorganopolysiloxane polymer of the formula:

    M.sup.Vi D.sub.t M.sup.Vi

where M^(Vi) is as previously defined, D is R₂ SiO_(2/2) units where Ris as defined above wherein the subscript t defines a polymer having aviscosity ranging from 100 to 200,000 centipoise at 25° C.; (c) aplatinum catalyst; and (d) a crosslinking or curing agent selected fromthe group consisting of hydrogen containing silanes, hydrogen containingpolysiloxanes and mixtures thereof.
 2. A fast curing low compression setsilicone polymer/resin composition as defined in claim 1 wherein saidD/Q ratio ranges from about 0.6:1 to about 5:1.
 3. A fast curing lowcompression set silicone polymer/resin composition as defined in claim 2wherein said D/Q ratio ranges from about 0.9:1 to about 2:1.
 4. A fastcuring low compression set silicone polymer/resin composition as definedin claim 1 further comprising a filler.
 5. A fast curing low compressionset silicone polymer resin composition as defined in claim 4 whereinsaid filler is selected from the group consisting of titanium dioxide,lithopone, zinc oxide, zirconium silicate, silica aerogel, iron oxide,diatomaceous earth, calcium carbonate, fumed silica, silazane treatedsilica, precipitated silica, glass fibers, magnesium oxide, chromicoxide, zirconium oxide, aluminum oxide, alpha quartz, calcined clay,asbestos, carbon, graphite, cork, cotton, synthetic fibers and mixturesof any of the foregoing.
 6. A fast curing low compression set siliconepolymer/resin composition as defined in claim 5 wherein said filler isselected from the group consisting of fumed silica, silazane treatedsilica, calcium carbonate and mixtures of any of the foregoing.
 7. Afast curing low compression set silicone polymer/resin composition asdefined in claim 1 further comprising from an inhibitor compoundselected from the group consisting of vinyl-containingorganocyclotetrasiloxane, trialkyl cyanurate, alkyl maleate, acetyleniccompounds and mixtures of any of the foregoing.
 8. A fast curing lowcompression set silicone polymer/resin composition as defined in claim 1further comprising at least an inhibitor compound having at least onehydroperoxy radical of the formula --C--O--O--H.
 9. A thermally stablegasket having a low compression set and comprising a heat curedcomposition as defined in claim
 1. 10. A thermally stable gasket havinga low compression set and comprising a heat cured filled composition asdefined in claim 1.